1. Field of the Invention
The present invention relates to an image processing apparatus and method and a signal switching output device for performing processing of doubling the number of scanning lines of a field. More specifically, the invention relates to an image processing apparatus and method for generating one field in which the number of scanning lines has been doubled by using a plurality of fields as well as to a signal switching output device that is used in such an image processing apparatus.
2. Description of the Related Art
A technique of increasing the vertical resolution of an image by increasing the number of scanning lines per field is known as a technique for improving the image quality in a TV signal transmission system. Line doubling devices that double the number of scanning lines per field are known as devices that perform such processing. Among the line doubling device is a type that generates one line-doubled field using three fields. This type of line doubling device rearranges three input fields and processes, at an arbitrary time point, only fields obtained from one frame. This line doubling device is configured based on an algorithm that is optimized for line doubling on an ordinary camera source input having different motion phases for respective fields.
FIGS. 1A and 1B show images that are obtained before and after line doubling processing by the line doubling device. The line doubling device produces a line-doubled image shown in FIG. 1B based on a pre-processing image shown in FIG. 1A.
On the other hand, for example, to convert interlaced images having 525 scanning lines per frame (525i) into progressive images having 525 scanning lines per frame (525p), processing that utilizes inter-field correlation or intra-field correlation is generally performed.
Where the input is a camera source of (525i, for example, images of five consecutive fields A, Bxe2x80x2, C, Dxe2x80x2, and E are different from each other as shown in FIG. 2. Fields A, C, and E are odd-numbered fields of frames and fields Bxe2x80x2 and Dxe2x80x2 are even-numbered fields of frames.
In converting images of 525i into images of 525p, progressive images having 525 scanning lines per field are obtained by combining interlaced images of field A (scanning lines: 262.5) and field Bxe2x80x2 (scanning lines: 262.5) that are consecutive and whose contents vary as time elapses.
As a result of the above processing, the number of scanning lines per field is doubled. Since the image contents of the consecutive fields vary as time elapses, the vertical resolution of combined images (frames) is also doubled.
Incidentally, where input images as a subject of line doubling processing are from a film source, no effective result is obtained even if line doubling processing is performed by the above line doubling device. The reason is as follows.
NTSC TV systems are of 30 frames per second (60 fields per second) while film sources of movies etc. are usually of 24 frames per second. Therefore, to convert a film source into a TV signal, number-of-frames conversion processing such as 3-2 pull-down (3:2 pull-down) processing is generally performed.
The 3-2 pull-down processing is such that a reading operation of reading out the first one of two consecutive frames of a film source as three fields of a video signal and reading out the next frame as two fields is repeated. For example, as shown in FIG. 3, the first frame is read out as three fields A, Axe2x80x2, and A of a video signal and the next frame is read out as two fields Bxe2x80x2 and B of the video signal. In this manner, in the 3-2 pull-down processing, consecutive fields having the same image contents are produced in numbers 3, 2, 3, 2, 3, . . . to form a video signal.
Therefore, in an NTSC signal obtained by the 3-2 pull-down processing, motion (a motion phase) occurs every three or two fields. As a result, the line doubling device having the algorithm that is based on the assumption that different motion occurs every field cannot perform effective line doubling processing on an NTSC signal obtained by such 3-2 pull-down processing.
Conversion into a PAL signal is performed likewise in such a manner that 50 fields are generated each second from 24 frames of a film source. Since motion occurs every two fields, the line doubling device cannot perform effective line doubling processing either on a PAL signal obtained by converting a film source in this manner.
It is seen from the above description that the following problems occur if line doubling processing is performed on fields generated by such processing as the 3-2 pull-down or the 2-2 pull-down by using the above-described line doubling device that generates one line-doubled field from three fields.
The line doubling device handles fields as having different images though they have the same image actually. Therefore, with an NTSC signal obtained by the 3-2 pull-down processing, it is not recognized that a line-doubled image signal is one obtained from three fields of the same frame.
Further, the resolution decreases if intra-field processing is performed with an assumption that images of consecutive fields to be processed are different from each other.
Further, once the line frequency (line rate) is doubled, original film images cannot be restored any more.
To attain best image quality in restored original images, each frame of a file source should be processed as a still frame. However, the conventional line doubling device does not perform such processing. That is, although each frame (consisting of two or three fields) of a film source needs to be processed as a still frame, the line doubling device does not operate so as to realize the highest resolution when original images are restored.
The only method for solving the above problems is to redesign the line doubling device totally. However, this is costly and takes time.
The present invention has been made in view of the above circumstances, and an object of the invention is therefore to provide an image processing apparatus and method and a signal switching output device capable of performing line doubling processing by using a line doubling device without causing deterioration.
To solve the above problems, an image processing apparatus according to the invention comprises signal switching output means for receiving sequential input fields and for outputting, based on the sequential input fields, a plurality of fields obtained from the same image; and line doubling means for generating one line-doubled field using the plurality of fields that are output from the signal switching output means.
In the image processing apparatus having the above configuration, the signal switching output means receives sequential input fields and outputs, based on the sequential input fields, a plurality of fields obtained from the same image. The line doubling means generates one line-doubled field using the plurality of fields that are output from the signal switching output means.
In this manner, in the image processing apparatus, the line doubling means generates one line-doubled field using a plurality of fields obtained from the same image.
An image processing method according to the invention comprises a field output step of receiving sequential input fields and outputting, based on the sequential input fields, a plurality of fields obtained from the same image; and a line doubling step of generating one line-doubled field using the plurality of fields that are output by the fields output step.
In this manner, in the image processing method, the line doubling step generates one line-doubled field using a plurality of fields obtained from the same image.
A signal switching output device according to the invention receives sequential input fields and outputs, based on the sequential input fields, a plurality of fields obtained from the same image to line doubling means for generating one line-doubled field using the plurality of fields.
With this signal switching output device, the line doubling means generates one line-doubled field using a plurality of fields obtained from the same image.